Numerical constraints on XML data

Boundaries occur naturally in everyday life. This paper introduces numerical constraints into the framework of XML to take advantage of the benefits that result from the explicit specification of such boundaries. Roughly speaking, numerical constraints restrict the number of elements in an XML data fragment based on the data values of selected subelements. Efficient reasoning about numerical constraints provides effective means for predicting the number of answers to XQuery and XPath queries, the number of updates when using the XQuery update facility, and the number of encryptions or decryptions when using XML encryption. Moreover, numerical constraints can help to optimise XQuery and XPath queries, to exclude certain choices of indices from the index selection problem, and to generate views for efficient processing of common queries and updates.We investigate decision problems associated with numerical constraints in order to capitalise on the range of applications in XML data processing. To begin with we demonstrate that the implication problem is strongly coNP-hard for several classes of numerical constraints. These sources of potential intractability direct our attention towards the class of numerical keys that permit the specification of positive upper bounds. Numerical keys are of interest as they are reminiscent of cardinality constraints that are widely used in conceptual data modelling. At the same time, they form a natural generalisation of XML keys that are popular in XML theory and practice. We show that numerical keys are finitely satisfiable and establish a finite axiomatisation for their implication problem. Finally, we propose an algorithm that decides numerical key implication in quadratic time using shortest path methods.     

The implication problem for ‘closest node’ functional dependencies in complete XML documents

With the growing use of XML as a format for the permanent storage of data, the study of functional dependencies in XML (XFDs) is of fundamental importance in a number of areas such as understanding how to effectively design XML databases without redundancy or update problems, and data integration. In this article we investigate a particular type of XFD, called a weak ‘closest node’ XFD, that has been shown to extend the classical notion of a functional dependency in relational databases. More specifically, we investigate the implication problem for weak ‘closest node’ XFDs in the context of XML documents with no missing information. The implication problem is the most important one in dependency theory, and is the problem of determining if a set of dependencies logically implies another dependency. Our first, and main, contribution is to provide an axiom system for XFD implication. We prove that our axiom system is both sound and complete, and we then use this result to develop a sound and complete quadratic time closure algorithm for XFD implication. Our second contribution is to investigate the implication problem for XFDs in the presence of a Document Type Definition (DTD). We show that for a class of DTDs called structured DTDs, the implication problem for a set of XFDs and a structured DTD can be converted to the implication problem for a set of XFDs alone, and so is axiomatizable and efficiently solvable by the first contribution. We do this by augmenting the original set of XFDs with additional XFDs generated from the structure of the DTD.     

Consistent data for inconsistent XML document

XML document may contain inconsistencies that violate predefined integrity constraints, which causes the data inconsistency problem. In this paper, we consider how to get the consistent data from an inconsistent XML document. There are two basic concepts for this problem: Repair is the data consistent with the integrity constraints, and also minimally differs from the original one. Consistent data is the data common for every possible repair. First we give a general constraint model for XML, which can express the commonly discussed integrity constraints, including functional dependencies, keys and multivalued dependencies. Next we provide a repair framework for inconsistent XML document with three basic update operations: node insertion, node deletion and node value modification. Following this approach, we introduce the concept of repair for inconsistent XML document, discuss the chase method to generate repairs, and prove some important properties of the chase. Finally we give a method to obtain the greatest lower bound of all possible repairs, which is sufficient for consistent data. We also implement prototypes of our method, and evaluate our framework and algorithms in the experiment.     

XML data update management in XML-enabled database

With the increasing demand for a proper and efficient XML data storage, XML-Enabled Database (XEnDB) has emerged as one of the popular solutions. It claims to combine the pros and limit the cons of the traditional Database Management Systems (DBMS) and Native XML Database (NXD). In this paper, we focus on XML data update management in XEnDB. Our aim is to preserve the conceptual semantic constraints and to avoid inconsistencies in XML data during update operations. In this current era when XML data interchange mostly occurs in a commercial setting, it is highly critical that data exchanged be correct at all times, and hence data integrity in XML data is paramount. To achieve our goal, we firstly classify different constraints in XML documents. Secondly, we transform these constraints into XML Schema with embedded SQL annotations. Thirdly, we propose a generic update methodology that utilizes the proposed schema. We then implement the method in one of the current XEnDB products. Since XEnDB has a Relational Model as the underlying data model, our update method uses the SQL/XML as a standard language. Finally, we also analyze the processing performance.     

Dependency-preserving normalization of relational and XML data

Having a database design that avoids redundant information and update anomalies is the main goal of normalization techniques. Ideally, data as well as constraints should be preserved. However, this is not always achievable: while BCNF eliminates all redundancies, it may not preserve constraints, and 3NF, which achieves dependency preservation, may not always eliminate all redundancies. Our first goal is to investigate how much redundancy 3NF tolerates in order to achieve dependency preservation. We apply an information-theoretic measure and show that only prime attributes admit redundant information in 3NF, but their information content may be arbitrarily low. Then we study the possibility of achieving both redundancy elimination and dependency preservation by a hierarchical representation of relational data in XML. We provide a characterization of cases when an XML normal form called XNF guarantees both. Finally, we deal with dependency preservation in XML and show that like in the relational case, normalizing XML documents to achieve non-redundant data can result in losing constraints.     

不完全信息环境下存在XML强多值依赖的XML文档规范化研究

不完全信息环境下XML文档中的数据存在多值依赖时.为了避免在没有约束条件下XML文档数据出现冗余及更新异常,引入XML强多值依赖的概念和理论对XML文档的规范化进行了系统研究.基于节点信息等价、节点信息相容的概念给出了XML强多值依赖的定义;基于层次化的XML强多值依赖,提出了不完全XML文档树满足XML强多值依赖范式的条件;给出了满足该条件的不完全XML文档树无数据冗余的判定定理;提出了不完全XML文档树的规范化算法,对其时间复杂性进行了分析.理论研究和实例分析表明:研究成果较好地解决了在不完全信息环境下XML文档中存在层次化的XML强多值依赖引起的数据冗余问题.     

Binary equality implication constraints, normal forms and data redundancy

We define binary equality implication constraints (BEICs) in relational databases and study the implication problem of these constraints, in particular, we provide a sound and complete set of inference rules for a common subset of BEICs. Two normal forms with respect to BEICs are defined and shown to be necessary and sufficient to prevent different types of data redundancies that may be caused by these constraints.     

一个基于粗糙集的XML函数依赖发现算法

数据依赖是数据库的一个重要概念。函数依赖是一种常见的数据依赖关系,是数据语义的重要组成部分。随着XML文档的大量出现,这一概念被引入到XML的领域中。本文在约束限制范围的基础上,给出了XML函数依赖的定义。引入粗糙集解决XML数据不完整的特点,给出XML函数依赖的判定定理。并且提出了一个发现XML文档中最小非平凡函数依赖的算法。该算法基于一致集的概念,通过不可分辨关系划分元组集减少求一致集的运算次数,使用逐层求精的算法来计算最小非平凡XML函数依赖集的左部。通过该算法得到的XML函数依赖的语义信息对数据存储模式设计、查询优化和更新异常检查来说是十分重要的。     

XML结构完整性约束的研究

XML的结构完整性约束用来表示元素之间或路径之间的结构关系,它们在XML查询优化中有着举足轻重的作用。提出了基于元素的结构完整性约束和基于路径的结构完整性约束的概念,定义了排他性包含、必需性包含、路径蕴涵、路径互斥和路径同现的语法和语义,研究了它们的性质以及它们与DTD的关系,在此基础上,给出了将不能用DTD表达的结构完整性约束添加到DTD中的方法。     

Dynamically Updating XML Data: Numbering Scheme Revisited

Almost all existing approaches use certain numbering scheme to encode XML elements to facilitate query processing when XML data is stored in databases. For example, under the most popular region-based numbering scheme, the starting and ending positions of an element in a document are used as the code to identify the element so that the ancestor/descendant relationship between two elements can be determined by merely examining their codes. While such numbering scheme can greatly improve query performance, renumbering large amount of elements caused by updates becomes a performance bottleneck if XML documents are frequently updated. Unfortunately, no satisfactory work has been reported for efficient update of XML data. In this paper, we first formalize the XML data update problem by defining the basic operators to support most XML update queries. We then present a new numbering scheme that not only requires minimal code-length in comparison with existing numbering schema but also improves update performance when XML data is frequently updated at arbitrary positions. The fundamental difference between our new scheme and existing ones is that, instead of maintaining the explicit codes for elements, we only store the necessary information and generate the codes when they are needed in query processing. In addition to present the basic scheme, we also discuss some optimization techniques to further reduce the update cost. Results of a comprehensive performance study are provided to show the advantages of the new scheme.     

Updating XML views published over relational databases: Towards the existence of a correct update mapping

XML data management using relational database systems has been intensively studied in the last few years. However, in order for such systems to be viable, they must support not only queries, but also updates over virtual XML views that wrap the relational data. While view updating is a long-standing difficult issue in the relational context, the flexible XML data model and nested XML query language both pose additional challenges for view updating.

This paper addresses the question, if for a given update over an XML view, a correct relational update translation exists. First, we propose a clean extended-source theory as criteria for determining whether a given translation mapping is correct. To determine the existence of such a correct mapping, we classify a view update as either un-translatable, conditionally or unconditionally translatable under a given update translation policy. This classification depends on several features of the XML view and the update: (a) granularity of the update at the view side, (b) properties of the view construction, and (c) types of duplication appearing in the view. These features are represented in the Annotated Schema Graph. This is further utilized by our Schema-driven Translatability Reasoning algorithm (STAR) to classify a given update into one of the three above update categories. The correctness of the algorithm is proven using our clean extended-source theory. This technique represents a practical approach that can be applied by any existing view update system in industry and academia for analyzing the translatability of a given update statement before translation of it is attempted. To illustrate the working algorithm, we provide a concrete case study on the translatability of XML view updates.     

Updating Recursive XML Views of Relations

This paper investigates the view update problem for XML views published from relational data.We consider XML views defined in terms of mappings directed by possibly reeursive DTDs compressed into DAGs and stored in relations. We provide new techniques to efficiently support XML view updates specified in terms of XPath expressions with recursion and complex filters.The interaction between XPath recursion and DAG compression of XML views makes the analysis of the XML view update problem rather intriguing.Furthermore,many issues are still open even for relational view updates, and need to be explored.In response to these,on the XML side,we revise the notion of side effects and update semantics based on the semantics of XML views,and present efficient algorithms to translate XML updates to relational view updates. On the relational side,we propose a mild condition on SPJ views,and show that under this condition the analysis of deletions on relational views becomes PTIME while the insertion analysis is NP-complete.We develop an efficient algorithm to process relational view deletions,and a heuristic algorithm to handle view insertions.Finally,we present an experimental study to verify the effectiveness of our techniques.     

Optimizing updates of recursive XML views of relations

XML publishing has been an emerging technique for transforming (portions of) a relational database into an XML document, for example, to facilitate interoperability between heterogeneous applications. Such applications may update the XML document and the source relational database must be updated accordingly. In this paper, we consider such XML documents as (possibly) recursively defined XML views of relations. We propose new optimization techniques to efficiently support XML view updates specified via an XPATH expression with recursion and complex filters. The main novelties of our techniques are: (1) we propose a space-efficient relational encoding of recursive XML views; and (2) we push the bulk of update processing inside a relational database. Specifically, a compressed representation of the XML views is stored as extended shared-inlining relations. A space-efficient and updatable 2-hop index is used to optimize XPATH evaluation on XML views. Updates of the XML views are evaluated on these relations and index. View update translation is handled by a heuristic procedure inside a relational database, as opposed to previous middleware approaches. We present an experimental study to demonstrate the effectiveness of our proposed techniques.     

XML数据库更新语言的定义和实现

目前人们对XML数据的管理系统研究的焦点主要集中在XML数据的存储和查询,但作为完整的数据管理系统,还需要提供对XML数据库系统的更新操作。论文提出一种称为U_XMLSQL的针对XML数据库的更新语言,接着设计了一种高效的物理存储结构对XML数据进行关系存储,在此存储结构的基础上设计并实现了更新语言中定义的基本操作,最后通过实验验证此存储方法和更新算法的高效性。     

Reasoning about keys for XML

We study absolute and relative keys for XML, and investigate their associated decision problems. We argue that these keys are important to many forms of hierarchically structured data including XML documents. In contrast to other proposals of keys for XML, we show that these keys are always (finitely) satisfiable, and their (finite) implication problem is finitely axiomatizable. Furthermore, we provide a polynomial time algorithm for determining (finite) implication in the size of keys. Our results also demonstrate, among other things, that the analysis of XML keys is far more intricate than its relational counterpart.     

Partitioning methods for multi-version XML data warehouses

Due to an explosive increase of XML documents, it is imperative to manage XML data in an XML data warehouse. XML warehousing imposes challenges, which are not found in the relational data warehouses. In this paper, we firstly present a framework to build an XML data warehouse schema. For the purpose of scalability due to the increase of data volume, we propose a number of partitioning techniques for multi-version XML data warehouses, including document based partitioning, schema based partitioning, and cascaded (mixed) partitioning model. Finally, we formulate cost models to evaluate various types of queries for an XML data warehouse.     

XML数据的B树存储实现及更新

XML正逐渐成为 WWW数据表示和交换的标准 ,如何有效实现对于 XML数据的存储、查询及更新等操作是 XML 相关技术研究中的一个重要领域。本文首先简要介绍了我们的基于模式匹配的 XML 数据库系统 (DISXDBS)组成 ;然后研究了如何实现用 B树存储 XML 文档以及对其进行查询、更新等操作 ;最后与目前存在的几种 XML 文档的存储策略进行比较。     

DTD模式下的XML结构完整性约束

XML结构完整性约束(XSICs)描述了XML文档中节点或路径之间结构关系,这种约束可以看成是DTDs的扩展和补充.定义了元素排他性包含、必需性包含、路径蕴含、路径同现和路径互斥五种XSICs的语法和语义,研究了如何使用XSICs扩展DTDs,并解决了有DTDs的情况下结构完整性约束的逻辑蕴含问题和一致性问题.     

XML压缩文档上的数值更新方法

近年来,XML已成为Web上信息交流和资源共享的主要载体。但XML自身的自冗余特性限制了它的普遍应用。目前,已经有研究成果提出了XML的压缩方法。压缩的XML文档能够有效利用存储空间,节省网络带宽。在实际应用中,经常需要对压缩存储的XML文档进行更新。对于大的压缩文档,如果先解压再更新,会消耗大量时间,因此,高效的更新方法应该避免解压缩文档,在压缩的XML文档上直接进行更新操作。本文针对压缩XML文档中的数值类型（包括整型和浮点型）数据,研究了在保持压缩状态条件下如何进行有效的数值更新,提出了基于XPRESS实现的Naive数值更新方法,以及修改XPRESS编码方法实现的更为高效的Pivot数值更新方法。通过大量的实验证明,Pivot数值更新方法不仅能够提供高效的更新处理,而且保持了XPRESS的高压缩率。     

Mapping DTDs to relational schemas with semantic constraints

XML is becoming a prevalent format and standard for data exchange in many applications. With the increase of XML data, there is an urgent need to research some efficient methods to store and manage XML data. As relational databases are the primary choices for this purpose considering their data management power, it is necessary to research the problem of mapping XML schemas to relational schemas. The semantics of XML schemas are crucial to design, query, and store XML documents and functional dependencies are very important representations of semantic information of XML schemas. As DTDs are one of the most frequently used schemas for XML documents in these days, we will use DTDs as schemas of XML documents here. This paper proposes the concept and the formal definition of XML functional dependencies over DTDs. A method to map XML DTDs to relational schemas with constraints such as functional dependencies, domain constraints, choice constraints, reference constraints, and cardinality constraints over DTDs is given, which can preserve the structures of DTDs as well as the semantics implied by the above constraints over DTDs. The concepts and method of mapping DTDs to relational schemas presented in the paper can be extended to the field of XML Schema just with some modifications in related formal definitions.